This invention relates to an electric fuse, and more particularly to such a fuse which can be bolt mounted or clip mounted.
Current limiting power fuses generally have a cylindrical housing of insulating material which is closed at each end by a metal terminal cap. A main fusible element(s), usually a silver ribbon, extends inside the housing between the terminal caps. The space around the fusible element is filled with silica sand. When current through the fuse exceeds the rating of the fuse for a sufficient time, the element melts, or fuses at one or more points, causing the formation of an arc. The arc progressively melts the sand and forms channels of fulgurite in it. The relatively high resistance fulgurite eventually suppresses any significant flow of current through the fuse.
The melting of the main fusible element is generally silent, and hence, not noticeable. Thus, it is common to provide indicating means by which it can be readily determined if the main fusible element has melted. Generally, such indicating means include movable indicator mechanisms such as those described in U.S. Pat. No. 3,895,338, issued July 15, 1975 to Gray et al and assigned to the assignee of the present application, and in U.S. Pat. No. 2,797,279, issued June 25, 1967 to Brandt et al.
In operation, such fuses are generally clip mounted or bolt mounted, depending upon the particular application. Both clip mounting and bolt mounting operation exhibit advantages and disadvantages.
Presently, most fuses are clip mounted wherein spring loaded clips firmly grasp conductive cylindrical ferrules which are disposed in electrically contacting relation adjacent to the fuse terminal caps. Such clip mounted fuses can be simply inserted and removed. However, for some fuse applications, the clip mounted fuse exhibits several disadvantages. One such disadvantage arises as a result of space limitations in the electrical cabinet in which the fuses are installed. More particularly, in order for a fuse clip to make good electrical contact to the fuse ferrule, the clip must be rather rugged. Also, in order to provide the simple insertion/removal feature of the clip mounted fuse, the clip structure generally includes protruding ears. The protruding ears function to guide the ferrules during fuse insertion, allowing the clip to open and then properly seat the ferrules. In view of the foregoing, where space limitations exist, the presence of such a clip structure is undesirable. Another disadvantage associated with the use of clip mounted fuses is that it is generally impractical to clip mount a second fuse, i.e., couple a second fuse to the first fuse. Such coupling is desirable for those situations in which the current rating of the first clip mounted fuse is too small.
Bolt mounted fuses are generally bolted between a pair of conductive mounting bus bars. An advantage of such a bolt mounted fuse is that bolt mounted fuses generally provide tighter electrical contact surfaces than clip mounted fuses. As a result, bolt mounted fuses usually exhibit reduced heating as compared to clip mounted fuses. Another advantage of a bolt mounted fuse is that it is generally convenient to bolt mount a second fuse in those situations in which the current rating of the first bolt mounted fuse is too small.
Whether the fuse is clip mounted or bolt mounted, in successfully performing their intended function, such fuses have to be replaced. There is little problem in obtaining a replacement fuse for a clip mounted fuse or a replacement fuse for a bolt mounted fuse. However, there is a significant problem in obtaining a single space conserving replacement fuse which can be either clip mounted or bolt mounted. In this connection, although additional bolt mounting structure could be added to the widely employed clip mounted fuse, such structure would undesirably increase the size of the fuse. Also, such additional bolt mounting structure generally presents impediments which make clip mounting of such a fuse impractical. Further, such additional bolt mounting structure may require additional processing of the clip mountable fuse, i.e., welding, brazing or soldering, in order to modify the clip mounting fuse to make it suitable for bolt mounting operation. Such additional processing is undesirable as it increases the assembly cost of the fuse.
Accordingly, it is a general object of this invention to provide an electric fuse which can be either clip mounted or bolt mounted.
It is another object of this invention to provide such a fuse in which the bolt mounting feature is obtained without increasing the size of the clip mounted fuse.
It is another object of this invention to provide such a fuse in which the bolt mounting feature is obtained through processing which does not require welding, brazing or soldering.